If you mean a function that detects whenever Claire’s sprite appears and then swaps it out, then maybe there’s a way. I’ll have to look into it some more, but I think if it isn’t doable via basic in-game eventing then there might be a script that does what you’re suggesting, which would be fantastic. Either way, I’ll see what I can find! It’s worth noting that some cutscenes do change very slightly based on whether or not Abby and/or Vespa have gained weight, but ideally I’ll add some more functionality like that in the future.
I know the part you’re talking about with the hookshot, as it’s frustrated a few people. Honestly, there’s one chest on each of the two paths there, and neither of them contain anything unique or extremely valuable, so I don’t think it’s worth starting from the very beginning on that account. I’ve tried not to make a habit of doing that in areas you can’t come back to so that players don’t feel like they’re missing too much.
There’s definitely a lot of potential for alchemical-type interactions between items like the melon and kelp! For now I’m keeping that part of the game as simple as I can while I focus on more plot-driven elements, but it’s something that has a lot of room to grow as the game develops more, I think. Don’t worry though, none of the bubble kelp interactions lower approval rating; it’s just for fun! I picture Claire as the type who doesn’t indulge in stuff like that for the most part, so it’d be unexpected from another party member’s point of view to see her on bubble kelp. That said, I think there is potential for more content tied to subsequent uses, but again, we’ll see how that goes as the game progresses!